The objective of wind energy is to generate electricity from the wind using wind turbines at maximum possible efficiency and minimum cost. Said wind turbines basically consist of a tower, a nacelle which contains the electrical generator,
and a rotor comprising at least two blades.
The tower supports all the elements incorporated in the nacelle and transmits to the foundations all the reaction forces generated as a consequence of the wind turbine's different aerodynamic actions and operating conditions.
Generally, given the dimensions of the wind turbine and consequently, of the tower, the latter is manufactured using modular sections of reinforced concrete called precast segments. To join these precast segments it is necessary to use a filler material, which may consist of mortar (also called grout) or a resin, deposited in them.
From now onwards the invention will be explained making reference to the use of mortar as filler, although it could be, as mentioned, resin or another material.
During the assembly of concrete towers at low temperatures it is necessary to guarantee minimum temperature conditions (at least 5° C.) for both the precast segments and the mortar before pouring the mortar, including the temperature of the mortar poured into the vertical and horizontal joints, to guarantee adequate curing so that the mortar can develop all its mechanical properties (resistance).
When these assemblies are made at low temperatures, where the temperature can drop to −20° C., in order to ensure a correct structural behaviour of the towers, it is necessary to have a heating system that allows the temperature to be maintained above 5° C. in both the precast segments and the mortar poured into the joints.
Pouring mortar at ambient temperatures below 0° C. is always a fairly restrictive conditioning factor. This is due to the fact that concrete requires a certain temperature for the cement to hydrate and acquire resistance. Also, because it contains water, there is a risk that when it starts to set, free-running water freezes increasing its volume, with the ensuing danger of cracking.
In the case of assembling concrete towers at low temperature, the volume of mortar is insufficient to guarantee that the water will not freeze, as it is totally surrounded by a large mass of prefabricated concrete which is at ambient temperature.
In low temperature conditions (below 5° C.) in addition to ensuring the mechanical properties of the mortar, it is necessary to guarantee the perfect filling of the joints between the precast segments that make up the tower.
To this effect, it must be feasible to pump said mortar to a height of 20 m with no segregation occurring upon pouring it from a height of 20 meters in free fall, in the case of vertical joints. Horizontal joints are even more restrictive as in this case, the pouring of the mortar must be guaranteed at heights above 100 m. It is required for all mortars, according to their technical datasheet, that the temperature of the support (in the case of towers for wind turbines these are the precast segments) is at a temperature of at least +5° C. to guarantee correct curing. Below 5° C. manufacturers do not guarantee the necessary minimum resistances.
Traditionally, in the closest prior art, foundations are made at −20° C. using concrete with high cement content so that it has a high heat of hydration and heats up quick enough to avoid freezing. Generally, footings are covered with thermal blankets so as not to lose too much heat and in this way maintain the temperature at the required values.
The problem with using thermal blankets is that they need to adhere well to the surfaces that require heating. If said blankets are not well-adhered, the heating of the surfaces is slow and non-homogeneous.
Another possibility for heating consists of using fans with an electrical resistance (cylindrical conduits with directional air outlet nozzles) directed towards the joints. Some of the problems that arise with this solution are that a high number of fans is necessary, making it necessary to have a high number of generators to supply energy to the fans, and that a certain assurance of continuous system operation is necessary as a stoppage would entail the rapid loss of the thermal conditions previously generated.
Other alternatives considered in the pre-heating are the use of infrared lamps. The market solutions do not achieve effective results where heating is concerned.
The current technique for pouring mortar presents four clear drawbacks, among which one would highlight the problems with cracking due to freezing of the water present, quality problems in the formation of the joints, filling problems (especially in horizontal joints at heights that are distant from the ground), and problems with the resistance capacity of the mortar when the temperature reached is below 5° C., problems with assembly in relation to both times and means employed (difficulty with pumping, heating of the nearby medium where the mortar is deposited . . . etc.), and the need to use special mortars with a high content in cement with the ensuing increase in the expensiveness of the tower.
The heating system known in the state of the art designed to the thermal conditioning of the materials to resolve the problems described above present a high consumption due to low thermal efficiency.